Definitions
Precision -Made so as to vary minimally
from a set standard.
Mensuration - The act, process, or art of measuring. Measurement of
geometric quantities.
Resolution - Smallest difference between indications of
a displaying device that can be meaningfully distinguished.
For a digital display device, this is the change in the indication when the
least significant digit changes by one step.Accuracy - Closeness of the agreement between the result of the measurement &
the
true value of the measurand.Measurand - A quantity that is being determined
by measurement.

A wooden holder
for ⅜" stemmed digital & dial
indicator gages. Many tools are supplied with their
own
indicator.
Two came with dial indicator comparator stands & two with gun cartridge
measurement
fixtures. 2nd from the front is my first digital-style gage which was replaced by the front gage that
has much
higher resolution.
The gages vary by their respective measurement ranges, accuracies, &
resolutions.

Their positions are offset to accommodate the lug back mounts.
The plungers of the more costly units are not compressed while stored.

Several two-inch range gages were used on various machines before changing to
advanced DROs.
For example, I used two gages just for the
Taig
micro lathe & to good effect, providing excellent control.
I liked it so much I went digital for both X &
Z-axes but later extensively modified the
lathe to be CNC.
Surprising accuracy & repeatability though low durability, but given the cost,
acceptable if on a budget.

A two-inch range digital indicator that reads to 0.0005"
resolution. It has an 8mm stem.

The fine adjustment mechanism for the stand.

A collar was made to adapt the 8mm stem to ⅜". The screw is threaded
through to directly contact the stem.

Different types of dial gage interchangeable 4-48 threaded
indicator points.
To keep from straining or breaking a gage's internal alignment pin, completely
depress the plunger
so the
rack absorbs the loosening & tightening forces before changing the points. Never use
Loctite.

Z-axis offset animation showing a ¾" end mill being set at 4.000" above the vise
bed.
Starrett also makes a superior (expensive) 4-inch
special dial depth gage for
Z-height setting.

A 3.000" height offset gage using a 40 mm (1.5")
diameter face Mahr dial indicator (GER) that reads to 0.0005".
Stem is 8mm (.315"). The 7.5mm (0.295") diameter flat tip is an ideal shape. The
bracket is all steel construction.
All critical surfaces of the parts, including the round post ends, were
precision surface
ground for high accuracy.
An adjustable, brass, over-travel
stop was added so the needle can only turn about one revolution.
This height gage design has excellent sensitivity for delicate end mills & does
not require a lot of Z.

The bottom of this Z-offset gage
needed lapping which was performed on a granite
surface plate first using
320 followed 400 & 600 grit silicon carbide papers. Moved the part in a figure-8 pattern to insure an even
removal of material. Significant surface improvement resulted. The edges were
deburred
with an India stone.

This offset gage has a magnetic bottom which attracts debris
& the spring is too strong for very small end mills.

1-2-3 Jo-blocks bolted together make a very accurate, low-cost
zeroing fixture.

2" high Z-offset gage. A 3"
micrometer & a 1-2-3 Jo-block were used to set the gage's zero at
2.0000".
The recessed bottom required a Jo-block.
The micrometer was first locked at 3.0000" using the
gage
block.

Mill Z-offset gage (instructions)
used to set tool lengths.
Needle-based, Z-offset gages set the
mill more quickly & accurately than
illuminated types plus they are not damaged by over travel.

Animation showing a 2.000" Z-offset height being set on the
Taig CNC Z-axis using the Mach3 MPG step mode.

With the gage light illuminated, the value (1.0000") was then
entered into the Z-axis of the mill DRO.

Here the electric gage is working on the
CNC Taig mill's anodized table. The connection was
completed by grinding off the black anodize on the T-nut inner face & making
multiple punch marks.
The vise should not clamp the gage that is deep in the jaws as that would short-out
the upper & lower plates.

The punch
marks are raised & sharp thereby piercing the table's inner T-slot anodized
surface to complete
the connection. Though maybe not necessary, this can be done for all the T-nuts
that hold the vise in place.

A tooling plate is mounted
onto the anodized table where a 0.2 ohm conductivity is realized via 6, T-nuts.

The gage can also be used with parallels & lightly clamped into the vise.

A Mitutoyo digital micrometer head combined with a hardened &
precision-ground depth base.
Note: Over tightening the setscrew can distort the mounting flange & bind the
mechanism.

The scale is not reversed like its mechanical counterpart,
but digital micrometers can
be zeroed at any location & then the negative sign is simply ignored for the
readings.
Hardened & precision-ground depth base attached to a Mitutoyo digital
caliper.Digital depth gage with a large base.
See digital caliper manual.

Starrett No. 3751 digital height gage.
Auto-off in 5 minutes but retains zero; auto-on when the slide
is moved.
Zero to 6.45" max range, 0.0005" (0.01mm)
resolution & ±0.001" (± 0.03mm)
accuracy.
Supplied with an extra
scribe & clamp plus an excellent, padded, aluminum hard case.
The vertical
column is set-in from the tip
of the base's nose for better
stability. This height gage's compact size
is
especially valuable when measuring parts with
very small features or using it on my two mills.
The scribes
are not carbide-tipped.
The fine-edged, HSS scribes are limited to semi-hard metals &
the rounded tips
limit
scratch depth. This height gage is ideally suited for use on small, delicate
work.

Adjusting to a specific height can be accomplished by
picking it up & using it much like a regular caliper.
Slightly increasing the slide resistance of the transducer (a small, side
setscrew) helps adjustability.
Setting an exact numerical value with this type of adjustment mechanism is
slower than
that of a height gage equipped with a fine adjustment carriage mechanism.

A carbide-tipped (Mitutoyo)
10", dial height gage on a
granite surface plate (± 0.0001").High accuracy can be
achieved using
gage blocks to set specified heights. Use layout die to make the scribe marks easier to
see.Mitutoyo height
gage manual.
Surface plates are useful for precision alignment when
assembling parts, too.

Mitutoyo
OEM wooden case.

Depth attachment. Rod accepts different 4-48 threaded
indicator points. This was my first height gage.
It is easier to miss-read an analog dial than a digital readout though analog
scales can be interpolated.

Measuring distances between holes using a center-finder attachment
from Mitutoyo.

Telescoping & half-ball
Mitutoyo inside gage sets (Japan). The half-ball type can get into a shallow, blind
hole
better than a ball type.
Expand into hole, lock & then measure the gage with a micrometer or caliper.

Left: The small (half-ball) hole gage is
expanded by the center wedge.
Right: The telescoping inside gage posts spring outward, self-center & are then
locked via a knob on the handle.
They can then be accurately measured with a caliper or a micrometer.

A self-centering, 1.4" to 6" cylinder
bore gage (instructions).
The gage is first set up to measure a specific size (zeroed) then run through the bore
to measure its variation.
To keep the extensions in order, a vibrator engraver was used to label each size on
a non-critical surface.

The dial gage must be
inserted deep enough to preload (or move) the needle about 1 revolution
(0.050").
The black plastic shroud can be installed after calibration to protect the head
under heavy shop use.

These ½" travel digital indicators, preloaded to 0.050" depth, can also be utilized but
others may not work.

The center measurement anvil moves in & out.
The outside mechanism depresses under spring tension to center the head.

Small anvil animation.

Assemble the appropriate anvils & spacers (left side) for the
target measurement size.
Then, using a gage block, set a micrometer (e.g., 2") to the bore size & zero the dial
scale.
The gage is then run through the cylinder & the variation from set size, noted.

CalipersMitutoyo Absolute Digimatic caliper
(Japan).
An excellent digital caliper that is very accurate throughout its entire measurement
range.
Always maintains zero, large LC display, greater than 3 years battery life. No irritating auto-off.

Superior quality Mitutoyo (Japan) digital micrometer that reads down to 0.00005" or
0.001mm.
The scales are engraved, not chemically etched thus have superior readability &
durability.
Even if the battery is removed, the micrometer's scales allow it to be used as a
standard instrument.
It has a micro-polished, carbide-faced working surfaces & an effective spindle lock.DO NOT store a micrometer (any style) with its measurement
anvils touching.

12" micrometer shown with the standards case, open. The holes
lighten the instrument for easier handling.
I needed the 7", 8", & 9" micrometers (for e.g., a flywheel) so
it was more economical to buy the whole set.

I needed four, aluminum rods to be exactly 9.6250" in length so the
9"-10" micrometer was used.

Two micrometer sets covering the 0"
through 12" range. Eleven size standards; 1" through 11".
Two separate sets can make handling/storing the boxes easier than one big heavy 0" ~
12" set.

A 0.6" micrometer compared to a 12"
micrometer.

A micrometer head that can be
incorporated into other devices e.g., an
adjustable lathe carriage stop.
½" range. The tip of the 0.2" diameter anvil is rounded & hardened. The collar
is ⅜" diameter x 0.32" long.

Mitutoyo digital micrometer head.

Hub micrometer that measures 0-1" to 0.0001" & designed to clear through a ¾"
hole.
Handy in tight places especially in milling setups. A spindle lock would have
been better.

A 6" throated micrometer
having a measurement range of 0 to 1" maximum with a 0.0001" scale.

Locking levers made of metal are a plus for durability & precision of
the mechanism movement.

Caliper-type micrometer measures to 0.0001".
Measuring anvils are approximately
¾"
above the micrometer.
The thread mechanism that keeps the anvil from rotating also acts as a somewhat
effective lock.

Carbide-tipped, small faces or spline micrometer for measuring in tight areas.
0-1" range with 0.0001 scale.
The anvils are 0.0775" diameter.

Carbide-tipped, point micrometer for measuring in very tight areas. 0-1" range with 0.0001 scale.
Points have a radius of approximately 0.012".

Screw
thread micrometer with five different anvil pairs measure both
unified &
metric external pitch diameters.
0" to 1" measurement range with a 0.0001" scale.
The left anvil holder floats back & forth to allow zeroing then
it is locked
into place.
However, the anvil itself always floats rotationally to maintain ease of
measurement.

Tramming a steel part before boring in the mill. Zeroed
at front, back, left, right. Tables & spindle then locked.

Starrett surface gage &
Interapid dial test indicator on the
granite surface plate being zeroed
using a 1" gage block. If possible, move the part not the gage when
measuring a surface.

For highest
accuracy, the angle between the stylist & part surface should be as close to
12° as possible.

The wide-range (±0.060") Interapid held by the rigid, precise
Starrett is a nice combination on a surface plate.

Indicating the Parlec solid jaw, animation. The slot on the
top of the solid jaw can also be used.The Interapid indicator has 0.0005"
resolution. See instructions on how to
set tip geometry
& see illustration.
Here, the needle moves <0.0001" in the center
which is well below the manufacturer's vise spec.

Rugged LS Starrett No. 711 Last Word DTI
& attachments (USA).
One gradation = 0.001".
If needed, fast & easy to send back to Starrett for repairs. They stand behind their
products.
I have damaged it twice & Starrett quickly repaired it charging only a nominal
price for return postage.

Using Dial Test Indicators - Test
indicators are primarily used for the testing or checking of parts & for machine
setups.
Test indicators come in two types; the plunger style & the lever style. The
lever style is more adaptable to smaller,
confined working areas. The lever style differs in measuring because the lever
contact moves in an arc rather than in a
straight line, as in the plunger style. This can cause a slight inaccuracy
called cosine error, if reasonable care is not
used in setting the angle of the lever to the work piece. If, for example,
a lever was set off 20º more at the start of a
reading than it should have been, there could be an error of .0006” in a .010”
range (0.012mm in a 0.2mm range).
This is not important when zeroing-out, but only when looking for a measurement.
It is best to keep the contact at or near
90º to the direction of movement unless the manufacturer specifies another
angle (see illustration).
Test indicators
should always be “loaded” 1/10 to ¼ of a turn before measuring. Test
indicators are not hand-held absolute measuring
tools. They are comparative instruments that check & compare to known standards
or that are used to zero-out setups.

Noga
NF1018 indicator arm (Japan) with ⅜" & dovetail clamp.
This style arm is very quick & easy to set up plus it has very good rigidity.

Noga arm held by a modified,
V-groove tool post, mounted off the headstock side T-slot of the
Taig mill.
Setup shows indicating a work piece before rotating to a
specific cutting angle.
The Noga arm is good for aligning mills,
lathes & rotary tables.

Zero-set universal dial test gage attachment (import).

A Federal 0.0001", dovetail mount, DTI being used to
indicate the Parlec vise's solid jaw.

This style universal DTI holder gives a broad sweep
of the small 18" mill table.

IndicOL #178 (USA) DTI holder attaches an
indicator to the mill's spindle. Best in class attachment.
Dovetail or stem-style test dial indicators can be attached to this holder.

Thread GagesLeft to right: imperial & metric (yellow) screw thread gages (2),
fractional, & numbered drill bit gages.
These plate-type thread gages would be more accurate if they were two or three
times thicker.
Having just a few threads, it is easy to make an error. For example, 10-32 & M6-1 are very
similar threads.

This metric thread gage is 0.11" thick whereas the others are
0.08" thick.

These gages check both nuts & bolts. Metric are black oxide
& imperial are galvanized. Sizes are clearly
stamped & colored.
Superior to plate-type gages which use only a few threads per size for testing.

The red laser beam is used solely for aiming. An infrared (IR)
sensor actually measures the temperature.
The distance to spot ratio is 8:1., so for e.g., at a 16" (407mm) distance the
measurement area is 2" (51mm).